Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147335 times)

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Offline electrodacus

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No really, I am not sure what is going on here,but in general, this shape somehow slows down other air around the craft and thus converts this energy into a greater speed for the craft. So conservation is retained as the other air is slowed down. This could have to do with a strong negative energy source against the positive one, caused by the positive one.

What happens is that energy is stored as pressure differential (propeller uses some of the wind power to increase pressure differential).
This stored energy while vehicle is below wind speed is then used to accelerate for some limited amount of time above wind speed.

Offline gnuarm

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There is nothing wrong with that definition if you understand what it means.

What definition?  ::)   Where have you 'defined' power other than to say that it has no time dimension?

I need to say that since you think it has a time dimension.  I was refereeing to the definition you provided.
Power is just the rate at which energy is converted to another form so it is not containing time. The thing that contains time is energy.

So when I say 10W of braking power and I do not mention any time interval for witch this power is applied then time is not involved at all and no work it is being done.
You may know speed as in case A 2m/s and you can calculate force 5N but that is about all you can know. You can not say about any changes to vehicle speed or kinetic energy as time is not mentioned anywhere.
As soon as I say the 10W is applied for 1ms then you have the time and also the energy 0.01Ws and thus you can calculate what happens to vehicle over that time period including change in kinetic energy and speed.
To me it just seems you do not see power for what it is and it just seems you confuse that with Energy.

Power is in units of work per time, J/s.  The 10W already includes the time element as it is joules per unit time.  Joules is not defined with any regard to time.  It can be 10 W for one second or 1 W for ten seconds.  10 W is 10 J/s.  So that could be 10 joules in 1 second, or 100 joules in 10 seconds, but it is 10 joules per second. 

Interesting that neither work nor power are considered SI base units, but that's not important.  I don't know if this matters either, but NIST shows work (energy) as derived from force and distance.  They show power as defined by work per unit time (J/s). 

NIST Diagram

Does that help?
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Offline gnuarm

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What brought it home for me was when the video talked about the difference in ground speed and air speed.  The wheels are working at ground speed while the propeller is dealing with the wind speed.  The higher ground speed means the "gearing" (including the propeller pitch, et. al.) allows the faster ground speed to create less resistance than the force generated by the prop. 

As others have pointed out the propeller blows air backwards from the car reducing the wind speed and lowering the wind's energy content conserving energy.

That should cover it, no?
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Offline electrodacus

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Power is in units of work per time, J/s.  The 10W already includes the time element as it is joules per unit time.  Joules is not defined with any regard to time.  It can be 10 W for one second or 1 W for ten seconds.  10 W is 10 J/s.  So that could be 10 joules in 1 second, or 100 joules in 10 seconds, but it is 10 joules per second. 

Interesting that neither work nor power are considered SI base units, but that's not important.  I don't know if this matters either, but NIST shows work (energy) as derived from force and distance.  They show power as defined by work per unit time (J/s). 

NIST Diagram

Does that help?

Sorry not sure where you have this wrong definition of what power and energy is.
Power is measured in Watt
Energy measured in Joules
Applying a power of 10W for one second will result in 10J or what I prefer 10Ws.
So the 10W includes not time is just a rate of work nothing to do with time while Energy includes time thus why I prefer to use Ws instead of Joules.
One Joule is power of 1W applied for 1 second but can also be 10W applied for 100ms or 1kW applied for 1ms. You get the idea that power has nothing to do with time it is the rate at witch work is done.

Not sure why Power and Energy are so misunderstood and the way they are defined by NIST is juts super bad and understandably confusing.
Why will you ever define Power using Energy ?

No wonder why so many are confused about how blackbird works.

Offline gnuarm

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Here's a thought experiment.  Instead of wind and a propeller, what if the wind were a conveyor belt and the prop were another wheel on that conveyor belt? 

Now the wheels can be geared so the ground movement applies a force to the conveyor belt.  Can the car move forward faster than the conveyor belt? 

Yes, as the conveyor ramps up speed the car would be propelled faster than the conveyor from the start.  Give the wheels a 2:1 gear ratio and the car will move at twice the conveyor speed.  Like with the propeller, the ground wheels turn faster, so the conveyor wheels can exert more torque resulting in a net forward force. 

This is stirring a memory of some toy I had years and years ago.  It also is making me wonder if that could be used for something practical.
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Offline electrodacus

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What brought it home for me was when the video talked about the difference in ground speed and air speed.  The wheels are working at ground speed while the propeller is dealing with the wind speed.  The higher ground speed means the "gearing" (including the propeller pitch, et. al.) allows the faster ground speed to create less resistance than the force generated by the prop. 

As others have pointed out the propeller blows air backwards from the car reducing the wind speed and lowering the wind's energy content conserving energy.

That should cover it, no?

No that will not cover it and is a completely wrong explanation.
Not only the explanation is wrong what it implies never actually happen in reality.

It is enough to look at my example with vehicle below speed A, vehicle at wind speed B and vehicle above wind speed C to see what happens and why their explanation can not work.
Look at C and notice that the way that both road and wind moved in the vehicle reference frame there is no chance for vehicle to move from left to right.
This examples are just there to eliminate the magic of propellers and air that people seem to not understand and also to show that without energy storage no wind power vehicle can exceed wind speed.
That also means that Blackbird will be above wind speed for a few minutes at most then start to slow down as the stored energy is used up.


Offline electrodacus

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Here's a thought experiment.  Instead of wind and a propeller, what if the wind were a conveyor belt and the prop were another wheel on that conveyor belt? 

Now the wheels can be geared so the ground movement applies a force to the conveyor belt.  Can the car move forward faster than the conveyor belt? 

Yes, as the conveyor ramps up speed the car would be propelled faster than the conveyor from the start.  Give the wheels a 2:1 gear ratio and the car will move at twice the conveyor speed.  Like with the propeller, the ground wheels turn faster, so the conveyor wheels can exert more torque resulting in a net forward force. 

This is stirring a memory of some toy I had years and years ago.  It also is making me wonder if that could be used for something practical.

I already did just that see the earlier replay. I used treadmills but conveyor belts as the same thing.
No the vehicle can not move faster than the conveyor belt unless you have an energy storage device.
See the end half of my video for details on how energy storage is used for a direct upwind vehicle


Offline gnuarm

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Power is in units of work per time, J/s.  The 10W already includes the time element as it is joules per unit time.  Joules is not defined with any regard to time.  It can be 10 W for one second or 1 W for ten seconds.  10 W is 10 J/s.  So that could be 10 joules in 1 second, or 100 joules in 10 seconds, but it is 10 joules per second. 

Interesting that neither work nor power are considered SI base units, but that's not important.  I don't know if this matters either, but NIST shows work (energy) as derived from force and distance.  They show power as defined by work per unit time (J/s). 

NIST Diagram

Does that help?

Sorry not sure where you have this wrong definition of what power and energy is.
Power is measured in Watt
Energy measured in Joules
Applying a power of 10W for one second will result in 10J or what I prefer 10Ws.
So the 10W includes not time is just a rate of work nothing to do with time while Energy includes time thus why I prefer to use Ws instead of Joules.
One Joule is power of 1W applied for 1 second but can also be 10W applied for 100ms or 1kW applied for 1ms. You get the idea that power has nothing to do with time it is the rate at witch work is done.

Not sure why Power and Energy are so misunderstood and the way they are defined by NIST is juts super bad and understandably confusing.
Why will you ever define Power using Energy ?

No wonder why so many are confused about how blackbird works.

There is nothing wrong with anything I've said.  All the examples you give agree with my post entirely.  The error is in your thinking that somehow time is associated with energy.  You can pervert the units as much as you want, but a joule is a unit of energy or work that has no time factor in it. 

I see you talk about "rate" of work.  That is the same thing as J/s.  In this context rate implies time.  So work is independent of time as shown by your examples above.  The same work results from different powers with different times, but the products must always be the same.  Why?  Because power is a rate, a function of time and must be multiplied by time to get work... to eliminate the time factor in work.

Do you think the same way about speed and distance?  Speed is analogous to power and distance is analogous to work.  Speed times time is distance, power times time is work.  Do you consider distance to be a function of time?  The only difference is we usually don't have a particular name for speed, rather it's distance per time like miles per hour, although they do use knots.  So is distance Knot·hours? 

I suppose none of this is going to matter.  You seem to be pretty entrenched in your thinking.  That's fine.  We can agree to disagree.
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Offline electrodacus

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There is nothing wrong with anything I've said.  All the examples you give agree with my post entirely.  The error is in your thinking that somehow time is associated with energy.  You can pervert the units as much as you want, but a joule is a unit of energy or work that has no time factor in it. 

I see you talk about "rate" of work.  That is the same thing as J/s.  In this context rate implies time.  So work is independent of time as shown by your examples above.  The same work results from different powers with different times, but the products must always be the same.  Why?  Because power is a rate, a function of time and must be multiplied by time to get work... to eliminate the time factor in work.

Do you think the same way about speed and distance?  Speed is analogous to power and distance is analogous to work.  Speed times time is distance, power times time is work.  Do you consider distance to be a function of time?  The only difference is we usually don't have a particular name for speed, rather it's distance per time like miles per hour, although they do use knots.  So is distance Knot·hours? 

I suppose none of this is going to matter.  You seem to be pretty entrenched in your thinking.  That's fine.  We can agree to disagree.

There is nothing wrong in what you said but.
While your example with speed and distance is a bit strange distance can not exist without time or more clearly space time are one single thing and not separate.
While speed is a rate same as power tho power includes speed so is a bit of a strange analogy.

What I was saying is that problem can be solved using power only and the result will be a net power that will also have a direction of action so 1d vector.
But doing the calculations this way without including time will give you just the rate of change and you need to add the time if you want more info on what happens with the speed over time for example or net power over time.


In any case the point I try to make is that no wind only powered vehicle traveling direct down wind or direct upwind can do that without using energy storage and it will need to use something other than the vehicle kinetic energy as that can not be used for this particular case where direction is either direct upwind or direct down wind.
For the direct down wind Blackbird the pressure differential energy storage is used and for direct upwind version small internal elastic storage or gravitational storage (depends on design) is used plus the stick slip hysteresis witch is the trigger to release stored energy multiple times a second.
That also means that for the direct down wind blackbird the vehicle will only be above wind speed for a limited amount of time.

Offline gnuarm

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I don't think I'm willing to watch a 25 minute video that is hard to understand when I find an error in the first four minutes.  You define the power from the wind as some stuff * (w-v).  You claim this is the reason why a propeller vehicle can't exceed the wind speed.  This ignores the rotation of the propeller which is the whole point! 

I also skipped ahead to 19 minutes where you claim the geared wheels and stick are not being analyzed correctly.   I don't see how you can say anything of the sort.  The analogy is not perfect between the propeller car and the gear car because the gear ratio of the gear car makes it move instantly while the propeller car has to accelerate to beat the wind speed. 

Maybe I'll watch the rest of this video someday, but for now it's just too much work. 

So how far would they need to drive the propeller car for you to say it's not running on stored power?
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Offline gnuarm

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Ok, if you are going to invoke relativity to discuss distance, then I think we will never find a common ground to discuss. 

Enjoy
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Offline electrodacus

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I don't think I'm willing to watch a 25 minute video that is hard to understand when I find an error in the first four minutes.  You define the power from the wind as some stuff * (w-v).  You claim this is the reason why a propeller vehicle can't exceed the wind speed.  This ignores the rotation of the propeller which is the whole point! 

I also skipped ahead to 19 minutes where you claim the geared wheels and stick are not being analyzed correctly.   I don't see how you can say anything of the sort.  The analogy is not perfect between the propeller car and the gear car because the gear ratio of the gear car makes it move instantly while the propeller car has to accelerate to beat the wind speed. 

Maybe I'll watch the rest of this video someday, but for now it's just too much work. 

So how far would they need to drive the propeller car for you to say it's not running on stored power?

w-v wind speed - vehicle speed is the wind relative to a vehicle driving directly down wind so absolutely the correct equation.
Propeller is nothing more than a wheel to travel trough a medium instead of the top surface of a medium like a regular wheel.

The wheel only vehicles will always be an analogy to direct up wind version only.
Because for direct down wind the air is required (air is a compressible fluid so energy can be stored) and that is how direct down wind blackbird actually works. Propeller is used to create a pressure differential and that is a way to store energy.

It depends on design. If you design it to accelerate slower thus spend more time below wind speed and store more energy then it can run for longer above wind speed.
Is easy to see that acceleration rate drops so you can calculate from that how long until it gets to peak speed and starts to slow down.
The v-w equation Derek used is wrong and will imply that vehicle acceleration rate increases while in all experiments done that was not the case.
Based on data Blackbird was super close to use all stored energy when it got around 30mph in that 2.8x wind speed record (that was more like 2x in reality).

Offline electrodacus

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Ok, if you are going to invoke relativity to discuss distance, then I think we will never find a common ground to discuss. 

Enjoy

That was maybe over the top but looking at speed or power as anything to do with time is also the wrong way to look at a rate of change.
This is of course a personal opinion but people do confuse Power with Energy and in many cases Force with Power.

Thus having a hard time understanding the problem I explained in the video and seen in the image below
This problem proves that w-v is the correct equation and also that without energy storage higher than wind speed is not possible.
If you disagree try and use v-w for all 3 cases and see what you get and if it make any sense. Clearly not what will happen in reality.

Offline Kleinstein

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What does output of the motor wheel mean ? This is not really clear to me.
It that the same as the power needed to supply the motor = the ouput power of the motor ?

For now it is just about the equation, so we don' t need to dicuss the 3 cases. We need to understand the equation first.

Output at the motor wheel is the input power in the motor from generator wheel plus the power that wind treadmill provide to that same wheel or subtract from the wheel as it is the case at C.
There are just two sources of energy available to vehicle one is the road treadmill and one is the wind treadmill. This is because we are looking in the frame of reference of the vehicle so vehicle is the reference thus is not moving.

You can salve the same problem in multiple way this is just the one I selected mostly based on the fact that people seems to prefer looking at this problem form the vehicle frame of reference and that is how Derek also solved this same problem.
You can look from the ground reference frame where ground / Road treadmill is not moving at 2m/s but vehicle moves forward at 2m/s left to right and in that case the wind treadmill will have moved at 6m/s the wind speed relative to ground/road but it will still be just 4m/s relative to vehicle.
The naming is a bit confusing, but it is OK to calculate this way, if the stick to the vehicle drawing frame as the reference and also use it for the rest of the calulation. In this case however we must have a closer look at the center part, especially the question, what is the meaning of P_net ?

edit:
Looking at it again, I realized that the formular is calculating the power in a difference reference frame. So I don't see a good way for calulating this way. It kind of lead nowhere. You get a number but no good way use to it, at least I don't see one.

The logical way is to calculate the power that is needed to power the motor, as that is what we would have to compare to the power from the generator.
« Last Edit: December 21, 2021, 10:40:38 am by Kleinstein »
 

Online PlainName

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We can agree to disagree.

What!??!!! After 958 comments? NOOOOOooooooo
 

Offline Brumby

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What happens is that energy is stored as pressure differential (propeller uses some of the wind power to increase pressure differential).
This stored energy while vehicle is below wind speed is then used to accelerate for some limited amount of time above wind speed.

I'm beginning to see where you might have overlooked something.

If I am right, what you said here makes sense, but there is an assumption you have made that is incorrect.  One which would lead you to a particular conclusion - that looks very much like the sort of thing you have been saying.
 

Offline Labrat101

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Also you have still forgotten they used a variable pitch propeller on blackbird  that If you had watch the video he said he pulled the handle by guess so the
exact angle between reverse & feathering is unknown but I guess it was between 13  16.5 degrees which would give the forward thrust .
 

So NO your formulae is wrong .   :-- :-- :-- :-- 

PS IF you are thinking of getting a new Job DON'T take up FLYing  .. :-DD
« Last Edit: December 21, 2021, 02:56:08 pm by Labrat101 »
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Offline gnuarm

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Quote
We can agree to disagree.

What!??!!! After 958 comments? NOOOOOooooooo

Lol

I didn't read the whole thread.  How long has electrodacus been insisting the car that goes down wind faster than the wind doesn't?  How long has he insisted energy involves time and power doesn't?

I find his arguments mildly entertaining.  The diagram posted seems to me to be a lot of fluff.  Especially amusing is his stored energy argument to explain "impossible actions" when it is just poor construction at work.  Then he says a better constructed model has "micro storage" of energy or something. 

If the wheels are geared 2:1, applying a force to the 1 wheel by moving the belt it is riding on will exert say 1 unit of force in the direction of the belt.  The gearing will result in twice the movement in the 2 wheel and half the force.  The two forces are opposite, so the vehicle has a half unit of force pushing it in the direction of the moving belt with the movement relative to the ground being twice the velocity of the movement of the belt.

I'm willing to say I'm wrong when someone shows that to me.  Happy to, in fact.  But someone who doesn't understand that "rate of change" in regards to values like power and energy fundamentally involves time can't possibly construct a rational argument.  While rate of change can refer to some other variable, in the case of power, it is the rate of change of energy wrt time.  Power involves time.  Energy does not. 

This is such an insane argument!  I won't argue with the guy because his arguments are so specious, yet I want so badly to help him understand.  But I'm not going to chase impossible dreams.  They guy clearly does not want to understand, so no one can help him.
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Offline Brumby

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A question, if I may....

Let's say the Blackbird has gone through all this "energy storage" exercise and has been running along the ground for long enough that the "stored energy" is all gone.  We are looking for the steady state where the speed is constant - no acceleration nor deceleration.  (I don't care how long this will take as we can imagine a test track as long as we want and a nice, consistent wind.)

electrodacus - what do you say it's speed will be?
 1. Greater than wind speed
 2. Equal to wind speed
 3. Less than wind speed
 

Offline gnuarm

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A question, if I may....

Let's say the Blackbird has gone through all this "energy storage" exercise and has been running along the ground for long enough that the "stored energy" is all gone.  We are looking for the steady state where the speed is constant - no acceleration nor deceleration.  (I don't care how long this will take as we can imagine a test track as long as we want and a nice, consistent wind.)

electrodacus - what do you say it's speed will be?
 1. Greater than wind speed
 2. Equal to wind speed
 3. Less than wind speed

This has probably already been posted, but there is a second video with much more detail that should convince any doubter.  It settled a $10,000 bet which was won by the guy making the video saying the downwind car will go faster than the wind. 



The car will ultimately run faster than the wind. 

In the first video the car was not just running faster than the wind, it continued to accelerate.  How much energy is stored in the pressure waves or whatever is imagined? 

It's a shame they don't have a larger test facility to clearly dispel this stored energy myth.
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Offline Labrat101

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It's from the variable pitch propeller that gives it the extra push . No magic involved.
How this works in real life . It does many early aviation used it on small low power crafts.
The new silent running drones use this method as well.
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Online IanB

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The naming is a bit confusing, but it is OK to calculate this way, if the stick to the vehicle drawing frame as the reference and also use it for the rest of the calulation. In this case however we must have a closer look at the center part, especially the question, what is the meaning of P_net ?

edit:
Looking at it again, I realized that the formular is calculating the power in a difference reference frame. So I don't see a good way for calulating this way. It kind of lead nowhere. You get a number but no good way use to it, at least I don't see one.

The logical way is to calculate the power that is needed to power the motor, as that is what we would have to compare to the power from the generator.

Actually, if you look at the car/wheel/belt system carefully, and make the following assumptions:

   1. The system is in steady state (no acceleration)
   2. The system is ideal (no friction losses from bearings or air resistance)

Then from these assumptions the power everywhere is zero, as power is only required to overcome losses or produce acceleration.

Since the power is everywhere zero, it is not possible to analyze this system in terms of power flows, and no conclusions can be drawn using that approach.

To analyze the system correctly, a different approach is required.
 

Online bdunham7

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To analyze the system correctly, a different approach is required.

As I pointed out much earlier, starting with reply #20 to this thread, you can pretty much explain it without much more than the principles of Archimedes.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Online bdunham7

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I didn't read the whole thread.

Don't, unless you want brain damage.

Quote
How long has electrodacus been insisting the car that goes down wind faster than the wind doesn't?  How long has he insisted energy involves time and power doesn't?

a) forever and b) that's a relatively recent claim

He has previously rejected Newton's laws of motion, the principles of Archimedes (simple machines, levers) and insisted that 'conservation of energy' somehow means 'conservation of kinetic energy' without even defining a closed system.  Now this, and the novel concept that work and energy are entirely distinct in a way that would matter in this particular case.  His main contentions seem to be that you can store a significant amount of energy in a localized pressure field in the uncontained atmosphere, and that the small-model experiments that clearly disprove his ideas are the result of energy storage due to 'stick-slip hysteresis'.
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Offline electrodacus

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A question, if I may....

Let's say the Blackbird has gone through all this "energy storage" exercise and has been running along the ground for long enough that the "stored energy" is all gone.  We are looking for the steady state where the speed is constant - no acceleration nor deceleration.  (I don't care how long this will take as we can imagine a test track as long as we want and a nice, consistent wind.)

electrodacus - what do you say it's speed will be?
 1. Greater than wind speed
 2. Equal to wind speed
 3. Less than wind speed

In the ideal case no friction direct down wind blackbird will get to designed wind speed higher than wind speed in an infinite amount of time same way a sail vehicle will take forever to get to wind speed (it will never quite get there).
In real world where there is friction at the point that remaining stored energy can no longer fully cover the friction losses the vehicle will start to slow down and the slow down part will take some time as now the kinetic energy will be the one supplying the losses.
The vehicle will continue to decelerate until it gets below wind speed and my best guess here is that it will get to some steady state below wind speed if it is in a perfectly constant wind but in real life outside wind variation is just super high so vehicle will accelerate again when it will get a wind gust so it will sort of oscillate between above wind speed and below wind seeped.
During that so called 2.8x wind speed record wind speed was between 8mph and 15mph so a fairly high variation and since a 2x increase in wind speed means 8x increase in available wind power the variation is just huge.


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